Numerically-controlled (N/C) and computer numerically-controlled (CNC) milling machines are well known to the prior art for providing automated milling processes. In both types of machines, the operations of a machine such as spindle position, spindle speed, feedrate of a work piece past the spindle, and so forth, are effected by a sequence of pre-programmed N/C instructions, one for each step of the milling process, which is contained in an N/C storage medium operatively interconnected with an N/C unit for the machine. For N/C milling machines, an N/C tape is used, and for CNC milling machines, central computer storage such as disc storage is used.
Adaptive control systems for modifying the commanded feedrate at each step in the milling process are also well known to the prior art, as typified by U.S. Pat. No. 3,728,595, Apr. 17, 1973, to Adams. In such adaptive control systems, a pre-programmed feedrate is lowered when the actual milling force in a step of the milling process exceeds a pre-programmed reference milling force. The pre-programmed reference milling forces and feedrates are obtained by use of a software routine which takes into consideration data such as the type of material of the work piece, the size of the cutting tool to be utilized, the maximum stock cross section of the work piece to be encountered, and characteristics of the milling machine, such as spindle stiffness, maximum spindle load, and machine horsepower. The set of reference milling forces comprise adaptive control system data and are conveniently combined with the N/C instructions, as are the feedrates, and accordingly placed in the N/C storage medium.
Although such adaptive control systems have greatly increased the productivity of the numerically-controlled milling machines with which they are used, for the reasons detailed in the aforementioned Adams patent, they have certain disadvantages. The modified N/C storage medium including the N/C instructions and adaptive control data has been usable only on the specific numerically-controlled milling machine for which the adaptive control system data was produced, inasmuch as other numerically-controlled milling machines may have widely differing stiffness, cutting load, or horsepower capacities. In many cases, a job providing for a specific milling process may have been originally planned for one type of machine or one particular machine, but rescheduled due to production requirements for another type of machine for which the adaptive control data will not provide acceptable feedrate control.
Also, radical milling conditions unforeseen at the time the adaptive control system data is produced may be encountered during the milling process. In particular, the reference milling force values for each step of the milling process provided by the software routine are highly dependent upon the accuracy of inputs provided by a human programmer relating to type of work piece material and so forth. Such undesirable behavior accordingly requires producing new adaptive control data by re-running the software routine and cannot be corrected at the milling machine itself.
It is accordingly an object of this invention to overcome the disadvantages of the prior art set forth above.
It is a further object of this invention to provide an improved adaptive control system which allows the use of the same adaptive control system data for a specific milling process on all milling machines capable of responding to the N/C storage medium in which the adaptive control system data is contained.
It is another object of this invention to provide such an improved adaptive control system which permits modification of the adaptive control system data at the milling machine without the necessity of reprogramming the N/C storage medium in which the adaptive control system data is contained.
It is yet another object of this invention to provide such an improved adaptive control system for use with numerically-controlled machine tools other than milling machines, including machines providing drilling, reaming, boring, tapping, and other processes.